The metal inserts in ferromagnetic material are used in different applications. They can be used as supporting elements of complex structures or as being part of particular single elements.
For example, the covering of a tyre has an internal insert of steel wires, which are criss-crossed to strenghten the whole structure.
Worn out tyres are covered with a new tread allowing in this way their recycling. The reconstructed tyre achieves, in this way, security levels which can be compared to a new tyre from any point of view. The application of stricts working procedures, from the acquisition and suitability testing of the structure, to very accurate pressure controls of the final product under working conditions, guarantees the high quality of the entire production process.
All wracks directed to reconstruction are in fact previously carefully examined through the utilization of suitable equipment, which verifies the conditions of suitability to reconstruction.
One of the main parameters taken into consideration is the integrity of the metal insert, which is usually tested through x-rays, ultrasounds equipments or through scirografy.
Unfortunately the non-destructive testing of ferromagnetic metal inserts using these appliances is rather expensive.
Two patents for non-destructive material tests are known, which make use of magnetism and electromagnetism. Patent US 2001/019263 describes an apparatus for testing the conditions of railroad rails. It consists in a wave generator/transmitter, inclusive of a solenoid, and in a wave receiver, also inclusive of a solenoid. Both have the same structure and each of them is enclosed.
This device includes a U-shaped box, representing the base and sides of the device itself. A guiding plate for the magnets develops orthogonal to the device along each end of the box. Each guiding plate is fixed to the two opposite sides. A L-shaped rolled section is in turn fixed to both the above mentioned guiding plates.
The box contains several magnets, the ends of which are held in the right position by the above mentioned guiding plates. Said rolled sections represent the magnet pole pieces. The box contains also several coils placed in a suitable shell. A covering plate is then fixed to the box, in order to occupy the side of the device facing the metallic insert to be examined. The measuring coils are positioned between the magnets and the metal insert, at the centre of the device. The box is equipped externally with at least a multiple signal power point. The box and the covering plate avoid the contact of the magnets and coils, respectively, with the operator's hands or with the object to be examined.
The inductor consists of pole pieces and permanent magnets made with long-lasting high-stability materials and placed on one or more planes parallel to the ferromagnetic metal insert to be examined. Each magnet is placed parallely to the sliding direction of the metal insert with respect to the device, object of this patent. When the device slides on the ferromagnetic metal insert, it is correct to say that each magnet is located parallely to the sliding direction of the device itself on the metal insert to be examined.
Each measuring coil is autonomously connected to the multiple signal power point. The coils can also have simple gears, which permit their rotation. It is therefore possible, later on, to direct them following the different angles of the metal layers with respect to the sliding axis of the object to be tested.
This device permits a non-destructive testing of the ferromagnetic insert, both on the surface and internal part of an object. The device creates a magnetic field, parallel to that of the insert itself. The position and the possible presence of a damage are identified by one or more coils that are placed in the magnetic field. The signals recorded by the coils are transmitted to a software obtaining a diagram which underlines the presence of defects (their position and extent).